Method and apparatus for detecting a projectiles flight path by sending a magnetic field produced by movement of frictionally imparted electrical change on the projectile

ABSTRACT

A method and an apparatus for measuring a flight path parameter of a projectile (7) or parts thereof during flight possibly into the region of the target, with the electrical charge imparted to the projectile (7) or its part by friction with the air and/or by the gas fumes generated during ignition or detonation being detected by means of at least one inductively operating sensor (1) and the zero passage of the resulting signal is evaluated. The resulting signal can be utilized to measure time of flight, velocity, a time pattern for the distribution of fragments or the like.

BACKGROUND OF THE INVENTION

The invention relates to a method and an apparatus for measuring aprojectile or parts thereof during flight, possibly into the targetregion.

Various methods are known in the ballistic measuring art to determinedifferent variables of interest with respect to a projectile or partsthereof. Optical measuring methods are dependent on the weather and thetime of day and are expensive. For inductive measuring methods, theprojectile must be magnetized which, however, is not always possible forthe most varied reasons, for example because the material is notmagnetizable (hard core projectiles or the like). Particularly inconnection with projectiles produced by explosion, no or only veryunsatisfactory results are obtained.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method and anapparatus for measuring a projectile or parts thereof, with such methodand apparatus being easy to operate, usable in many ways and permittingthe use of simple and inexpensive sensors.

This is accomplished by a method in which the electrical charge impartedto the projectile or its parts by friction with the air and/or by thegas fumes generated upon ignition or detonation is detected by means ofat least one inductively operating sensor, and the zero passage of theresulting signal is evaluated.

In this connection the fact is utilized that a projectile on its way tothe target receives an electrical charge from friction with the air.When passing the sensor or flying through the sensor, this charge, as aresult of the magnetic field generated by a moving charge, produces avoltage in the induction coil of the sensor in the form of a signalwhich passes through zero. This signal can be utilized to measure theflight time of the projectile in that the time between firing and theoccurrence of the zero passage is measured from which the velocity ofthe projectile can be determined. Moreover, the signal may actuate othermeasuring devices, e.g. target X-ray devices.

Additionally, the velocity of the projectile or its parts can bedetermined by the use of two or more sensors spaced one after the otherat predetermined intervals along the trajectory, with the timedifference between the zero passages of the signals of two sensorsarranged behind one another being measured.

The fragments of high-explosive projectiles or the like are alsoelectrically charged by the gas fumes of the detonator material and canbe measured accordingly, thus permitting the determination of a timeresolution of the cloud of fragments.

The method may be implemented by means of an apparatus which includes atleast one sensor equipped with an induction coil and disposed in theregion of the trajectory. This sensor is coupled with an evaluationdevice which retains at least the time of the zero passage of the signalgenerated by the sensor.

Further features of the invention will be found in the description belowand in the dependent claims.

The invention will now be described in greater detail with reference toembodiments that are illustrated in the attached drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of an apparatus for measuring aprojectile.

FIG. 2 is a schematic representation of the curve of a signal generatedby the sensor of the apparatus of FIG. 1.

FIG. 3 is a schematic representation of the use of a plurality ofsensors along the trajectory of a projectile.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The apparatus shown in FIG. 1 includes a sensor 1 in the form of aninduction coil 3 wound onto a frame 2, for example a simple woodenframe. Frame 2 may be provided with a circumferential groove 4 toaccommodate a few windings of the insulated wire forming induction coil3. Moreover, frame 2 may be provided with a stand 5 which facilitatesits placement. The area enclosed by induction coil 3 advisably lies in arange of about 1 to 6 m². Additionally, it is advisable to place frame 2as perpendicularly as possible to the direction of flight 6 of aprojectile 7 to be covered.

Induction coil 3 is connected to an adapter circuit 8 which may includea preamplifier 9, a filter 10, a muting device 11 and a line driver 12.By way of a line 13 and a line receiver 14, the signal generated by theinduction coil may be fed to an evaluation device 15, preferably aTransiscope, i.e. digital signal memory and screen display so that avisual evaluation can be made. Additionally, a computer 16 and/or atimer 17 may be connected to make an automatic evaluation.

If a projectile 7 flies closely past induction coil 3 or through it, apulse measurable at induction coil 3 has a maximum voltage in an orderof magnitude of a few 100 μV. FIG. 2 shows a voltage pulse as it isgenerated by induction coil 3 as a function of the time t and thetrajectory s, respectively. The time t₀ and the path s₀ on the abscissarepresent the point at which projectile 7 passes induction coil 3. Atthis point the signal would pass through zero if projectile 7 had aconstant electrical charge. Since, however, the electrical chargeincreases continuously due to the friction of the air, the zero passageof the signal is shifted somewhat to the right--with reference to thepath traversed in the direction of flight--toward t₁ and s₁,respectively. If this shift is lost in the measuring inaccuracy, it neednot be considered. However, if necessary, a respective correction can bemade since, for the same reason, the amplitudes of the positive andnegative branches of the signal do not have the same absolute maximumvalues U_(max), U_(min), so that a correction value for a determinationof the point in time t₀ of the passage of projectile 7 can becalculated, for example, by computer 16 from the differences between thetwo values.

If two or more sensors 1 are arranged at predetermined distances fromone another along the trajectory of projectile 7, see FIG. 3, thedifference in amplitudes can also be utilized for a determination of thechange in charge during flight of projectile 7 and thus for a correctionof the time difference between two zero passages of the signals from twosensors 1. If the trajectory of projectile 7 is long, the electricalcharge of the projectile approaches a maximum value so that a correctionof the zero passage is appropriate only at short distances of about 60to 80 m from the point of firing or detonation.

With an arrangement according to FIG. 3, the velocity of a projectile 7can be determined in various sections of its trajectory 18.

The measurement is independent of weather and time of day and does notrequire magnetization of projectile 7. Even if projectile 7 hitsinduction coil 3, an evaluatable signal is available since the zeropoint of the signal was reached. The measurements can also be made at adistance of a few meters from the point of detonation or the location offiring. The costs for induction coil 3 are very low so that it need notbe protected against damage. Tumbling projectiles and those turning endover end always produce pulses of the same polarity in contrast tomagnetized projectiles which have two magnetic poles. Projectiles havingelectronic fuses or internal electronic systems and in whichmagnetization would produce the danger of damage to the electronicsystem or actuate the fuse can be measured by way of their electricalcharges.

We claim:
 1. Apparatus for detecting a nonmagnetized projectile or partsthereof along its flight path, comprising: at least one sensor means,including an induction coil having a few windings arranged in a framewhich encloses an area in the range of substantially 1 to 6 m² anddisposed along the flight path of the projectile or parts thereof, forsensing the magnetic field produced by movement of the electric chargeof the projectile caused by air friction; and evaluation means, coupledto said coil, for detecting the zero passage of the signal generated insaid coil by said magnetic field.
 2. Apparatus according to claim 1,wherein said evaluation means retains at least the time of zero passageof the signal generated by said sensor means.
 3. Apparatus according toclaim 2, further comprising at least one additional said sensor means,with the two sensor means being arranged at a predetermined distance onebehind the other along the flight path of the projectile; and wherensaid evaluation means has a circuit for determining the length of thetime interval between the zero passages of the respective signals ofsaid two sensor means.
 4. Apparatus according to claim 2, wherein saidevaluation means further includes means for determining the extremeamplitude values of the signals from said sensor means.
 5. Apparatusaccording to claim 3, wherein said evaluation means further includesmeans for determining the extreme amplitude values of the signals fromsaid two sensor means.
 6. Apparatus according to claim 2, wherein saidframe includes support means for positioning said frame so that it issubstantially perpendicular to the direction of the flight path of theprojectile.
 7. Method for detecting a flight path characteristic of anonmagnetized projectile or parts thereof during flight comprising thesteps of: placing a coil, which has a few windings mounted on a frameenclosing an area in the range of substantially one to six squaremeters, in the region of the flight path of the projectile or partsthereof; sensing, by means of said coil, the magnetic field produced bymovement of the electrical charge imparted to the projectile or itsparts by friction with the air and/or the gas fumes produced duringignition or detonation; and evaluating the signal produced in the coilby said magnetic field by detecting at least the zero passage of saidsignal.
 8. A method as defined in claim 7 wherein said step ofevaluating includes determining and retaining the time of said zerocrossing.
 9. A method as defined in claim 8 wherein said step ofevaluating further includes determining the maximum amplitude values ofsaid signal on either side of the detected zero crossing, and utilizingsaid maximum amplitude values to provide a correction value for the timeof said zero crossing.
 10. A method according to claim 7 wherein saidstep of placing includes orienting the frame so that the windings extendsubstantially perpendicular to the direction of the flight path of theprojectile.
 11. A method as defined in claim 7, wherein said step ofevaluating includes utilizing the zero passage of the generated signalto measure the time of flight.
 12. A method as defined in claim 8,further comprising: arranging at least two of the frame mounted coilsone behind the other at a predetermined distance along the flight pathof the projectile; and utilizing the time difference between the zeropassages of the signals from the two coils disposed one behind the otherto determine the velocity of the projectile or its parts.